1. Field of the Invention
The present invention relates to a driving method for driving a plasma display panel of a matrix display type.
2. Description of the Related Background Art
In recent years, in association with enlargement of a display apparatus, a thin-type display apparatus has been required and various thin-type display apparatuses have been put into practical use. As one of the thin-type display apparatuses, attention is paid to a display apparatus using an AC (alternating discharge) type PDP (plasma display panel).
FIG. 1 is a diagram schematically showing an arrangement of a plasma display apparatus including a plasma display panel and its driving device.
As shown in FIG. 1, a PDP 10 is provided with m column electrodes D1 through Dm serving as data electrodes, and n row electrodes X1 through Xn and n row electrodes Y1 through Yn aligned to intersect with the respective column electrodes. Pairs of one row electrode Xi (1xe2x89xa6ixe2x89xa6n) from the electrodes X1 through Xn and one row electrode Yi (1xe2x89xa6ixe2x89xa6n) from the row electrodes Y1 through Yn are responsible for respective display lines of the PDP. The electrodes X1 through Xn and the row electrodes Y1 through Yn form respective display lines of the PDP so that one row electrode Xi (1xe2x89xa6ixe2x89xa6n) and one row electrode Yi (1xe2x89xa6ixe2x89xa6n) are in pairs for one display line. It is arranged in such a manner that the column electrode D and the row electrodes X and Y are placed to oppose each other with a discharge space filled with a discharge gas in between, and that a discharge cell corresponding to one pixel is formed at each intersection portion of the row electrode pairs and the column electrodes having the discharge space.
Herein, because each discharge cell emits light by exploiting a discharge phenomenon, it can take only two conditions: xe2x80x9ca light emitting conditionxe2x80x9d and xe2x80x9ca non-luminous condition.xe2x80x9d In other words, each can display only two levels of luminance: the lowest luminance (non-luminous condition) and the highest luminance (light emitting condition).
A driving device 100 performs a gradation driving using the subfield method with respect to the PDP 10 arranged as above in order to achieve a half-tone luminance display corresponding to an input video signal. According to the subfield method, an input video signal is converted into, for example, 4-bit pixel data corresponding to each pixel, and as shown in FIG. 2, a display period of one field is divided into four subfields SF1 through SF4 to respectively correspond to the bit orders of the pixel data. As shown in FIG. 2, each subfield is given with the number of light emissions (or a light emitting period) corresponding to their respective weights.
FIG. 3 shows various kinds of driving pulses that the driving device 100 applies to the row electrode pairs and the column electrodes of the PDP 10 within each subfield shown in FIG. 2 and the application timings.
As shown in FIG. 3, the driving device 100 initially applies a reset pulse PRx of a positive polarity to the row electrodes X1 through Xn and a reset pulse RPy of a negative polarity to the row electrodes Y1 through Yn. When these reset pulses PRx and RPy are applied, a reset discharge takes place in all the discharge cells of the PDP 10, whereby wall charges of a predetermined quantity are formed uniformly in each discharge cell. Consequently, all the discharge cells of the PDP 10 are initialized to be in a xe2x80x9clight emitting cellxe2x80x9d condition (collective reset step Rc).
Then, the driving device 100 separates the bit orders in the 4-bit pixel data into the subfields SF1 through SF4, respectively, and generates a pixel data pulse having a pulse voltage corresponding to the logical level of each bit. For example, in a pixel data writing step Wc in the subfield SF1, the driving device 100 generates a pixel data pulse having a pulse voltage corresponding to the logical level of the first bit of the pixel data. At this point, the driving device 100 generates a pixel data pulse having a pulse voltage at a high voltage when the logical level of the first bit is xe2x80x9c1xe2x80x9d, and generates a pixel data pulse having a pulse voltage at a low voltage (0 V) when the logical level of the first bit is xe2x80x9c0xe2x80x9d. Then, as shown in FIG. 3, the driving device 100 successively applies the pixel data pulses thus generated to the column electrodes D1 through Dm as one display line of pixel data pulse groups DP1 through DPn for each of the first through n-th display lines. Further, the driving device 100 generates a scanning pulse SP of a negative polarity as shown in FIG. 3 in sync with the application timing of each pixel data pulse group DP, and successively applies the same to the row electrodes Y1 through Yn. At this point, a discharge (selective erasing discharge) takes place only in the discharge cells at the intersections of the display lines applied with the scanning pulse SP and the xe2x80x9ccolumnsxe2x80x9d applied with the pixel data pulse of a high voltage, so that the wall charges formed within these discharge cells are lost. Consequently, the discharge cells initialized to be in the xe2x80x9clight emitting cellxe2x80x9d condition in the collective reset step Rc are changed to be in a xe2x80x9cnon-luminous cellxe2x80x9d condition. On the other hand, the selective erasing discharge does not take place in the discharge cells applied with the scanning pulse SP and a pixel data pulse of a low voltage, and therefore, these discharge cells are sustained in the condition initialized in the collective reset step Rc, that is, the xe2x80x9clight emitting cellxe2x80x9d condition. In other words, each discharge cell of the PDP 10 is set to either the xe2x80x9clight emitting cellxe2x80x9d or xe2x80x9cnon-luminous cellxe2x80x9d condition in response to the pixel data corresponding to the input video signal (pixel data writing step Wc).
Then, the driving device 100 repetitively applies sustain pulses IPx and IPy as shown in FIG. 3 to the row electrodes X1 through Xn and the row electrodes Y1 through Yn, respectively, in turn. The number of applications (or a period the application is continued) of the sustain pulses IPx and IPy applied during a light emission sustaining step Ic in each of the subfields SF1 through SF4 is, as set forth in FIG. 2, as follows given that xe2x80x9c1xe2x80x9d is the number of applications during the light emission sustaining step Ic in the subfield SF1:
Herein, only the discharge cells holding residual wall charges within their discharge spaces, that is, the xe2x80x9clight emitting cellsxe2x80x9d, discharge (sustained discharge) each time these sustain pulses IPx and IPy are applied. In other words, only the discharge cells in which the selective erasing discharge did not take place during the pixel data writing step Wc repeatedly emit light with the sustained discharge as many times as assigned to each subfield as described above, thereby sustaining the light emitting condition (light emission sustaining step Ic).
Finally, the driving device 100 applies an erasing pulse EP as shown in FIG. 3 to the row electrodes Y1 through Yn concurrently. When the erasing pulse EP is applied, an erasing discharge takes place in all the discharge cells of the PDP 10, and the residual wall charges in the discharge cells are all lost (erasing step E).
A series of operations composed of the collective reset step Rc, the pixel data writing step Wc, the light emission sustaining step Ic, and the erasing step E are performed in each of the subfields SF1 through SF4 shown in FIG. 2. According to this driving, light emissions with the sustained discharge are repeated a specified number of times corresponding to the luminance level of the input video signal throughout the display period of one field, and one can perceive the half-tone luminance corresponding to the number of light emission by sight. At this point, according to the gray scale driving based on the four subfields SF1 through SF4 as shown in FIG. 2, it is possible to display the half-tone luminance xe2x80x9c0xe2x80x9d through xe2x80x9c15xe2x80x9d in 16 levels (16-level of gray scale).
With a display apparatus using the subfield method described as above, a discharge readily occurs between the column electrodes and the row electrodes when an accumulative light emitting time of the PDP becomes longer. If the sustain pulses are applied to the column electrodes during the light emission sustaining step under these conditions, a discharge occurs between the column electrodes and the row electrodes in the discharge cells set in the non-luminous condition, which may possibly result in an erroneous discharge light emission between the row electrodes.
It is therefore an object of the present invention to provide a driving method of a plasma display panel for achieving a high-quality image display by preventing an erroneous discharge light emission between the row electrodes during the light emission sustaining step.
According to the invention, there is provided a method for driving a plasma display panel including a plurality of row electrode pairs each of which has a capacitive load between the row electrodes of each pair and a plurality of column electrodes arranged to intersect with the row electrode pairs to form a discharge cell at each intersection portion, to display an image with gradations in accordance with a video signal, the method comprising the steps of: forming a plurality of subfields into which a display period of one field in the video signal are divided, in each of the subfields, executing: a pixel data writing step for generating pixel data indicating one of a light emitting cell and a non-light emitting cell for each discharge cell of the plasma display panel in accordance with the video signal, for applying a scanning pulse to one row electrode in each pair of the plurality of row electrode pairs successively and for applying a pixel data pulse corresponding to the pixel data to each of the plurality of column electrodes in synchronism with the scanning pulse, so that each discharge cell becomes one of a light emitting cell condition and a non-light emitting cell condition corresponding to the pixel data; and a light emission sustaining step for applying a sustain pulse to row electrodes in each pair of the plurality of row electrode pairs alternately by the number of times corresponding to weights assigned to each of the subfields, so that only discharge cells which have become the light emitting cell condition in the pixel data writing step sustain discharge, and applying an address pulse to each of the column electrodes concurrently with a first sustain pulses which is a sustain pulse first applied during the light emission sustaining step, the address pulse and the first sustain pulse having a same polarity.
According to the invention, there is provided a method for driving a plasma display panel including a plurality of row electrode pairs each of which has a capacitive load between the row electrodes of each pair and a plurality of column electrodes arranged to intersect with the row electrode pairs to form a discharge cell at each intersection portion, to display an image with gradations in accordance with a video signal, the method comprising the steps of: forming a plurality of subfields into which a display period of one field in the video signal are divided, in each of the subfields, executing: a pixel data writing step for generating pixel data indicating one of a light emitting cell and a non-light emitting cell for each discharge cell of the plasma display panel in accordance with the video signal, for applying a scanning pulse to one row electrode in each pair of the plurality of row electrode pairs successively and for applying a pixel data pulse corresponding to the pixel data to each of the plurality of column electrodes in synchronism with the scanning pulse, so that each discharge cell becomes one of a light emitting cell condition and a non-light emitting cell condition corresponding to the pixel data; and a light emission sustaining step for applying a sustain pulse to row electrodes in each pair of the plurality of row electrode pairs alternately by the number of times corresponding to weights assigned to each of the subfields, so that only discharge cells which have become the light emitting cell condition in the pixel data writing step sustain discharge, and applying a discharge control pulse to one row electrode in each pair of the plurality of row electrode pairs concurrently with a first sustain pulse, which is a sustain pulse applied first to the other row electrode in each pair of the plurality of row electrode pairs during the light emission sustaining step, the discharge control pulse having a same polarity as the first sustain pulse and having a pulse width narrower than the pulse width of the first sustain pulse.